displaying a powerpoint presentation in the background of a video clip
Blender doesn't have support for reading powerpoint presentations. However you can save the presentation as a sequence of images and display the image sequence within blender.


In powerpoint choose "Save as" and select an image format.
In blender you can easily setup a plane to display the images with the import image as plane addon.
Adjust the texture to display an image sequence.




You can also find the same settings in blender internals image settings.